30 March 2019

"Zipper merging" is "the law"

Kate Thoma recently came upon a construction zone in Bloomington, and with traffic backed up in the left lane, she zoomed along in the unoccupied right lane until signs told her to move over. She was zipper merging, but her efforts were thwarted by a left lane vigilante who would not let her in line.

“I’m certain he thought of me as rude and entitled, but I was just doing what my 9th grade driver’s ed teacher taught me,” Thoma said.

Indeed zipper merging is the law, but Thoma’s experience prompted her to ask why Minnesotans can’t zipper merge and why some motorists get all worked up when people do it...

The Minnesota Department of Transportation in the early 2000s was the first in the nation to employ the zipper merge as a way to better manage traffic when a lane is closed in work zones. The concept is simple: Drivers remain in their respective lanes until they reach the designated merge point. Then, like we learned in kindergarten, drivers are supposed to take turns falling orderly in line.

“It’s a great idea in theory, but theory is not how people always drive,” said Dwight Hennessy, a traffic psychologist who teaches at Buffalo State College in New York. “Zipper works when everyone follows the rules — the system can handle the odd rule breaker — but typically when one person breaks those rules others often follow.”

When people speed by in the open lane, that ticks people off as those waiting in line for a long time perceive those passing by as being impatient rule breakers sneaking to the front, Hennessy said.

“It’s perceived unfairness,” said MnDOT work zone engineer Ken Johnson. “If more people would use lanes to the merge point, fairness is taken care of.”
Sometimes frustrated drivers take things into their own hands. Thoma has seen drivers intentionally blocking the open lane so nobody can pass. That’s a no-no, said Lt. Gordon Shank of the State Patrol, and a ticketable offense.
There's more information at the StarTribune.  Frankly I didn't realize it's "the law" (perhaps it varies by state).


  1. This situation is similar to a line at a grocery store. There is space to sneak forward ahead of 10 people queued up at the register. Why not form two lines with 5 people in each? Why wouldn't the last person cut in front of the line?

    If the traffic was backed up, then there was a bottleneck down in the only open lane (think a worker with a stop sign for an example). Regardless of how people merge in this case, the time to pass the zone for the cars at the tail-end of the queue will be the same. Just the space the cars take on the road will be different.
    But, if you are the _last_ car in a single file, being "smart" and cutting in at the front, you are making *everyone* wait for you now.

    Now, if everyone were already in two lanes zipper-merging, then it doesn't matter - because regardless of which lane you initially choose, you will end up somewhere toward the tail of the queue.
    But since for some reason the drivers "agreed" to form a single line, this makes the front-cutter an a*hole. (Not justifying the initial actions of the drivers, but they must've had some reason. Maybe they have already zipper-merged, ahead of time, and now you are cutting in the front...)

  2. In Las Vegas they have two-lane on ramps with a stop light in the middle that flips green and red between the two ramps effectively forcing a zipper merge. I thought it was really clever and I wonder why I don't see that more often.

    Also, in regards to VF's comment, here's a good video about waiting in line.


  3. The highway departments do not help by posting warnings signs for miles about the upcoming obstruction (ex "right lane closed in 2 miles", "right lane closed in 1 mile", etc). Basically, they are encouraging the early development of a single line. No warnings or just "traffic obstruction ahead" would encourage zipper merge.


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